A royal spokeswoman said the publication was "a clear breach of the couple's right to privacy".

"We are disappointed that photographs of the duke and duchess on a private holiday look likely to be published overseas. This is a clear breach of the couple's right to privacy," added the spokeswoman for St James's Palace.

The pictures were taken on the Caribbean island of Mustique where the duchess and her husband, Prince William, are on holiday. They are said to show the duchess, formerly Kate Middleton, walking in the surf alongside the prince.

It is unclear whether the photographer was on the island or whether they were taken from a boat offshore.

In September topless pictures of the Duchess taken at a French chateau were published in a French magazine, Closer. They were republished in other magazines, including Chi, and in the Irish edition of the Daily Star.

The existence of the pictures emerged over the weekend. The Sunday People, in an article headlined "Fresh agony over bikini snaps", reported that the pictures had been taken. The paper said it had "chosen not to view the pictures and, like the rest of the British media, will not publish them".

The incident echoes the treatment of the prince's mother, Princess Diana, when she was pregnant with William in 1982.

At the time she was on holiday on a Caribbean island when photographers from the Daily Star and the Sun snapped pictures of her in a bikini. The Press Council, the forerunner of the Press Complaints Commission, censured the papers for publishing the pictures.

• To contact the MediaGuardian news desk email media@guardian.co.uk or phone 020 3353 3857. For all other inquiries please call the main Guardian switchboard on 020 3353 2000. If you are writing a comment for publication, please mark clearly "for publication".

• To get the latest media news to your desktop or mobile, follow MediaGuardian on Twitter and Facebook